SafekipediaList of largest optical reflecting telescopes
Adapted from Wikipedia · Discoverer experience
This list shows the largest optical reflecting telescopes with mirrors 3.0 metres (120 inches) or bigger. These telescopes are measured by their aperture, which tells us how much light they can gather and how detailed their pictures can be. Some telescopes, like the Keck I and II used together, can work even better by using a special method called aperture synthesis through interferometry.
Being the largest doesn’t always mean a telescope is the best. For example, space-based telescopes like the Hubble Space Telescope fly above Earth’s atmosphere and can take clearer pictures over longer times. Where a telescope is placed on Earth also matters, because it affects which part of the sky can be seen and how often the telescope can be used.
The biggest telescopes on Earth use huge mirrors placed in special locations with steady air and good weather. They also use clever tricks like active optics and adaptive optics to fix blurry images caused by Earth’s air. These Earth-based telescopes can sometimes take even clearer pictures than the Hubble Space Telescope, and it costs less to update their tools and instruments.
Table of reflecting telescopes
This list shows big telescopes that use mirrors to collect light. These telescopes are sorted by how wide their main mirrors are, called the aperture. A bigger aperture means the telescope can gather more light and see details better.
Some telescopes have many small mirrors that work together, and they are ranked by how big all their mirrors are put together. Only telescopes with mirrors at least 3 metres wide are on this list, and they work with light we can see or that is just a little bit beyond red light.
Chronological list of largest telescopes
These telescopes were the biggest in the world when they were built, measured by how much light they can gather. Each one was the largest until a new, even bigger telescope was created.
The list shows the order in which these amazing tools were made, letting us see how technology has grown over time. Each telescope helped scientists discover new things about space.
| Years Largest | Name | Out | In | Aperture (m) | Area (m2) | M1 Mirror | Note | Altitude (m) |
|---|---|---|---|---|---|---|---|---|
| 2009–Present | Gran Telescopio Canarias |  |  | 10.4 | 74 | 36 × 1.9 m hexagons M1 mirror | Segmented mirror | 2267 |
| 1993–2009 | Keck 1 |  |  | 10 | 76 | 36 × 1.8 m hexagons M1 mirror | Segmented mirror, M1 f/1.75 | 4145 |
| 1976–1993 | BTA-6 |  |  | 6 | 26 | 605 cm f/4 M1 mirror | Mirror replaced twice | 2070 |
| 1948–1976 | Hale (200 inch) |  |  | 5.1 | – | 508 cm f/3.3 M1 mirror | 1713 | |
| 1917–1948 | Hooker (100 inch) |  | 2.54 | – | Also used for 1st optical interferometer | 1742 | ||
| For earlier entries, see List of largest optical telescopes historically | ||||||||
Future telescopes
These are telescopes that are either being built now or are being planned for the future. Once they are finished, they will join the list of the largest telescopes in the world.
Under construction
Telescopes that are currently being built include:
- Extremely Large Telescope, Chile – 39.5 m (1,560 in). Building started in 2018, and it is expected to start working in 2029.
- Thirty Meter Telescope, Hawaii, USA – 30 m (1,200 in). Building began in 2014 but stopped in 2015 and has not started again.
- Giant Magellan Telescope, Chile – will use seven mirrors to act like a single 21.4 m mirror. It is planned to start working in 2029.
- San Pedro Martir Telescope, Baja California, Mexico – 6.5 m (260 in). It is expected to start working in 2023.
- Magdalena Ridge Observatory Interferometer, New Mexico, USA – uses ten smaller telescopes together to act like one larger telescope. Building paused in 2019 because of money problems.
- Timau National Observatory, Indonesia – 3.8 m (150 in). Building expected to finish by early 2025.
Proposed
These telescopes are still being planned:
- Habitable Worlds Observatory (LUVOIR), a space telescope planned to launch in the early 2040s.
- MUltiplexed Survey Telescope (MUST), a 6.5 m telescope for studying stars and galaxies.
- Chinese Giant Solar Telescope (CGST), a telescope to study the Sun, with the power of a 5 m telescope.
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